1. Field of the Invention
This invention relates generally to anti-skid brake control systems for vehicles and more particularly to an anti-skid brake control system adapted for a vehicle having two or more independent fluid brake circuits with only one pressure reducing chamber and piston.
2. Description of Prior Art
In the prior art, such as, for example, U.S. Pat. No. 3,544,171 granted on Dec. 1, 1970, two independent fluid brake circuits (10, 11, 16a, 15a, 13a, 9a; 10, 11, 16b, 15b, 9b) are provided and each circuit has an anti-skid actuator 7a, 7b for independently actuating each brake circuit. Each of the actuators 7a, 7b comprises a brake fluid pressure control unit 18 which is actuated by an hydraulic servo 19 (column 4, lines 26-29 thereof).
This type of system, however, has serious drawbacks, one being that since the two actuators are provided within the respective brake circuits, the system itself is so complicated and large that an increase in cost is not avoidable. Another drawback is that once an anti-skid situation occurs, a considerable amount of fluid is necessary at one time, so that there might occur a lack of brake pressure when both actuators are actuated simultaneously.
Another prior art system, such as that disclosed in U.S. Pat. No 3,674,317 granted on July 4, 1972, includes two brake circuits (14, 18, 18'; 16, 26, 26') and a single anti-skid control unit 22. In this prior art system, however, the wheels (20, 20'; 28, 28') of both circuits are controlled by the single actuator 22, and therefore, the size of the actuator 22 must be sufficiently large so as to effectively control the pressurized fluid in the four wheel brake means 18, 18'; 26, 26'. In this case, a modulator valve assembly 30 is disposed within one (16, 26, 26') of the circuits so as to assist the pressure reducing operation in the wheel brake means 26, 26' in addition to the single actuator 22. Macduff, U.S. Pat. No. 3,724,915, is cited as being of interest and includes separate brake circuits with one servo notch, however it uses two separate pressure reducing chambers.